1. Field of the Invention
The present invention relates to a rotation-angle detecting device for detecting a rotation angle of a rotating body such as a motor, an image processing apparatus, and a rotation-angle detecting method.
2. Description of the Related Art
In an image processing apparatus such as a printer apparatus, a facsimile apparatus, a copying apparatus, a scanner apparatus, or a multifunction peripheral, a drive mechanism is driven by a drive motor, and thereby a unit necessary to perform image processing, such as an image reading operation or an image forming operation, is driven at predetermined speed.
Then, to drive the drive motor to rotate at intended speed, conventionally, the image processing apparatus connects a rotary encoder to a rotating shaft (a rotor) of the drive motor and causes the rotary encoder to output detection signals which are two-phase pulse signals with a quarter-cycle phase difference that varies according to a rotation angle of the rotating shaft, i.e., a rotation angle of the rotary encoder. The image processing apparatus detects a relative rotation angle from edge detection of the two-phase pulse signals and Hi/Lo states of the two phases, and controls a drive-motor driving signal, thereby driving the drive motor to rotate at intended speed.
This rotary encoder is, for example, a two-phase optical encoder including a disk with equally-spaced slits serving as optical windows formed on the periphery thereof and two photointerrupters placed at a distance of a quarter of the slit pitch of the disk. By binarizing signals output from the two photointerrupters, two-phase pulse signals can be obtained.
However, such a rotation-angle detecting device using an optical encoder needs components, such as a disk with slits and photointerrupters, and these components need to be mounted on a drive motor with high accuracy; therefore the rotation-angle detecting device has problems of increases in size and cost.
Accordingly, there has been proposed a magnetic-sensor-signal processing integrated circuit that finds relative rotation angle of two magnetic sensors placed at an offset angle of about 90 degrees relative to a magnetic field by using a vector represented by outputs from the two magnetic sensors, and includes a storage unit that stores therein sines and cosines in increments of a predetermined angle, a unit for rotating the vector in increments of the predetermined angle using the sines and cosines stored in the storage unit, and a unit for detecting a total rotation angle when the rotating unit has rotated the vector to a reference position (see Japanese Patent Application Laid-open No. 2004-191101).
That is, in this conventional technique, to find a relative rotation angle of two magnetic sensors placed at an offset angle of about 90 degrees relative to a magnetic field by using a vector represented by outputs from the two magnetic sensors, sines and cosines are stored in a storage unit in advance in increments of a predetermined angle. Then, the vector is rotated by using the sines and cosines stored in the storage unit, and a total rotation angle of the vector when having been rotated to a reference position is detected.
Incidentally, if an apparatus includes multiple drive motors, the cost can be reduced by using the same type of motors as much as possible. However, when the multiple drive motors are controlled with different resolutions, if control circuits or the like are installed to suit a motor controlled with a high resolution, the control circuit or the like is over-engineered for a low-resolution motor, and many high-performance control circuits are required, which results in an increase in the cost.
Furthermore, if several types of control circuits are installed to suit the different resolutions, the number of types of control circuits is increased, resulting in an increase in the cost as well. For example, in the above-described patent literature (Japanese Patent Application Laid-open No. 2004-191101), when the angle detection is performed with a different resolution for each motor, it is necessary to prepare rotation-angle detecting devices with different resolutions from one another.
In view of the above, there is a need to provide a rotation-angle detecting device capable of supporting multiple resolutions.